In a temperate climate, air temperature becomes relatively low during the winter season and relatively high during the summer season. For the climate, traditional houses had structures relatively well ventilated so that they are comfortable during the summer. In winter, the structures had the disadvantages that the interior of rooms takes a long time to become warm because of the influence of outside air when a heater is turned on to warm the interior temperature, and further cools off rapidly upon turning off the heater.
In recent years, the use of a heating and cooling equipment such as an air-conditioner has enabled the interior to be readily cooled and heated. For efficiency enhancement in a heating and cooling equipment, a house preferably has an airtight structure; thus, in a recent house the structure having good airtightness and further having a high heat-insulating property is adopted. The enhanced house airtightness has improved not only the efficiency of cooling but also that of heating.
A high heat-insulated house has a structure in which the heat caused by indoor living is also less easily exhausted to the outdoor, which leads to an increase of the room temperature due to the heat even in a state relatively low in outside air temperature and requires that the room temperature be forcibly reduced using an air conditioner.
Thus, there is a need for the development of a structure which maintains the airtightness of the house and reduces the cooling load or which exhausts the heat caused by indoor living to the outdoor without using an air conditioner.
Similarly, in recent automobiles, the improved airtightness has eliminated the indoor thereof getting colder in a state in which they are parked in the outdoors in winter, but, in summer, the indoor has an extremely increased temperature compared to the outside air.
The above-mentioned problems can be solved by using a material which not easily emits heat at lower temperature and easily emits heat when it reaches a certain temperature or higher.
Patent Documents 1 and 2 disclose an Mn-containing perovskite oxide represented by the compositional formula (A1−xBx)MnO3 as a thermal control device for suitably temperature-controlling equipment aboard a spacecraft such as an artificial satellite. The material is a phase-change substance which is an insulating substance in the higher-temperature phase and has a metallic property in the lower-temperature phase, and which has a larger heat-emitting amount in the higher-temperature phase and a smaller heat-emitting amount in the lower-temperature phase. Thus, the use of the material enables the above problems to be solved. In addition, the phase-change substance has a property in which a temperature (transition temperature) causing a change from the higher-temperature phase to the lower-temperature phase can be changed by modifying the composition ratio and further in which the heat-emitting amount rapidly decreases at the transition temperature or lower.
However, the phase-change substance represented by A1−xBxMnO3 disclosed in Patent Document 1 has a transition temperature of 280 to 300 K (about 10 to 30° C.). Here, when the phase-change substance is used as a house building material or the like, it is desired that it has a further increased transition temperature.
It is disclosed that increasing the mixing amount x can change the transition temperature from 250 K to 350 K. However, the substance has the disadvantage that increasing the mixing amount x to shift the transition temperature to higher temperatures allows the emittance change to tend to be mild and decreases the emittance change width Δε (ε at higher temperature−ε at lower temperature).    Patent Document 1: Japanese Patent Application Laid-Open No. 11-217562    Patent Document 2: Japanese Patent Application Laid-Open No. 2002-120799